The present invention generally relates to air filters. More particularly, this invention relates to non-mechanical filtering of small size particulate matter in air.
Air filtering systems to remove deleterious particulate matter are important for general health and particularly important for persons having allergies, asthmatic conditions and the like. Building air ventilation systems generally include air filtering means that requires the use of mechanical blowers and other large equipment. Air filter systems specifically designed to remove small size particulate matter also generally employ some type of mechanical air-moving equipment. Conventional window screens are generally limited to preventing the entry of insects and the like and therefore are not useful for filtering small particulate matter.
Various non-mechanical air filtering means have been proposed in the prior art. Such air filtering means generally function by capturing or collecting the particulate matter on or in a screening media. This results in a requirement that the filter be periodically cleaned or replaced. Where the air is heavily contaminated with particulate matter, such air filters must be cleaned or replaced quite often. U.S. Pat. No. 570,219 to Fletcher illustrates an air filtering systems of this type. In the Fletcher patent a filtering material is disclosed wherein warp-threads are interwoven to form closely-woven selvages. Dust or fine particles collect on the selvages and air passes between them. U.S. Pat. No. 1,056,722 to Adler discloses a dust-collecting screen consisting of a fabric formed from strands of coarse and linty textile adapted to be saturated with a non-evaporating liquid such as oil. The moistened linty textile collects small size particulate matter and air passes through the openings between the coarse and linty strands. In U.S. Pat. No. 2,478,097 to Glanzer a woven-screen air filter is shown having cloth-covered wire threads. The cloth covering for the wire threads collect particulate matter and may be saturated with a liquid to facilitate collection of dust and the like. U.S. Pat. No. 2,551,175 to Smith discloses a filter cloth formed from strands so tightly woven that filterable material will not pass through the inter-filament spaces of the woven strands and thereby limits air passage to the spaces between adjacent strands. U.S. Pat. No. 2,615,477 to Crawley discloses an air filtering media comprising woven fabrics formed entirely of yarns formed from continuous filaments of a vinyl resin and discontinuous filaments of a vinyl resin, the respective filaments alternating in a regular pattern throughout the fabric. U.S. Pat. No. 4,728,349 to Oshitari discloses a composite air filter medium comprising a glass fiber layer of desired dust-collecting efficiency and a supporting fiber layer of low dust-collecting efficiency. In U.S. Pat. No. 4,904,288 to d'Augereau a reusable air filter assembly is disclosed comprising a composite structure including an outlet stage filter medium consisting of two fabric layers woven in an egg-crate pattern.
The present Applicant has discovered that an air filter having at least 16% of the surface area open provides suitable natural ventilation. This structural limitation can be utilized to construct an air filter having openings sufficiently small to prevent the passage of small size particulate matter without collection or adhesion of the particulate matter in or onto the filter media while simultaneously permitting sufficient air flow for natural ventilation. It is further useful if an air filter medium having this characteristic can be provided in a structure that can be selectively disposed in a window frame or other opening.